FluidFM: Combining AFM and nanofluidics for single cell applications

FluidFM: Combining AFM and nanofluidics for single cell applications

The Atomic Force Microscope (AFM) is a key tool for nanotechnology. This instrument has become the most widely used tool for imaging, measuring and manipulating matter at the nanoscale and in turn has inspired a variety of other scanning probe techniques. Originally the AFM was used to image the topography of surfaces, but by modifying the tip it is possible to measure other quantities (for example, electric and magnetic properties, chemical potentials, friction and so on), and also to perform various types of spectroscopy and analysis. Increasingly, the AFM is also becoming a tool for nanofabrication.

Relatively new is the use of AFM in cell biology. We wrote about this recently in a Spotlight that described a novel method to probe the mechanical properties of living and dead bacteria via AFM indentation experimentations ("Dead or alive – nanotechnology technique tells the difference ").
Researchers in Switzerland have now demonstrated novel cell biology applications using hollow force-controlled AFM cantilevers – a new device they have called FluidFM.

"The core of the invention is to have fixed already existing microchanneled cantilevers to an opportunely drilled AFM probeholder" Tomaso Zambelli tells Nanowerk. "In this way, the FluidFM is not restricted to air but can work in liquid environments. Since it combines a nanofluidics circuit, every soluble agent can be added to the solution to be dispensed. Moreover, the force feedback allows to approach very soft objects like cells without damaging them."

As cell biology is moving towards single cell technologies and applications, single cell injection or extraction techniques are in high demand. Apart from this, however, the FluidFM could also be used for nanofabrication applications such as depositing a conductive polymer wire between to microelectrodes, or to etch ultrafine structures out of solid materials using acids as the spray agent. The team has reported their findings in a recent paper in Nano Letters ("FluidFM: Combining Atomic Force Microscopy and Nanofluidics in a Universal Liquid Delivery System for Single Cell Applications and Beyond").

Zambelli originally realized that the technology of the atomic force microscope that is normally used only to image cells could be transformed into a microinjection system. The result of the development by Zambelli and his colleagues in the Laboratory of Biosensors and Bioelectronics at the Institute of Biomedical technology at ETH Zurich and in the Swiss Center for Electronics and Microtechnology (CSEM) in Neuchâtel was the "fluid force microscope", currently the smallest automated nanosyringe currently in existence.

"Our FluidFM even operates under water or in other liquids – a precondition for being able to use the instrument to study cells" says Zambelli.

The force detection system of the FluidFM is so sensitive that the interactions between tip and sample can be reduced to the piconewton range, thereby allowing to bring the hollow cantilever into gentle but close contact with cells without puncturing or damaging the cell membrane.

On the other hand, if membrane perforation for intracellular injection is desired, this is simply achieved by selecting a higher force set point taking advantage of the extremely sharp tip (radius of curvature on the order of tens of nanometers).

To enable solutions to be injected into the cell through the needle, scientists at CSEM installed a microchannel in the cantilever. Substances such as medicinal active ingredients, DNA, and RNA can be injected into a cell through the tip. At the same time, samples can also be taken from a cell through the needle for subsequent analysis.

According to Zambelli, while this approach is similar to microinjection using glass pipettes, there are a number of essential differences.

"Microinjection uses optical microscopy to control the position of the glass pipette tip both in the xy plane and in the z direction (via image focusing)" he explains. "As consequence of the limited resolution of optical microscopy, subcellular domains cannot be addressed and tip contact with the cell membrane cannot be discriminated from tip penetration of the membrane. Cells are often lethally damaged and skilled personnel are required for microinjection."

"The limited resolution of this method and the absence of mechanical information contrast strongly with the high resolution imaging and the direct control of applied forces that are possible with AFM. Precise force feedback reduces potential damage to the cell; the cantilever geometry minimizes both the normal contact forces on the cell and the lateral vibrations of the tip that can tear the cell membrane during microinjection; the spatial resolution is determined by the submicrometer aperture so that injection into subcellular domains becomes easily achievable."

Experiments conducted by the Swiss team demonstrate the potential of the FluidFM in the field of single-cell biology through precise stimulation of selected cell domains with whatever soluble agents at a well-defined time.

"We confidently expect that the inclusion of an electrode in the microfluidics circuit will allow a similar approach toward patch-clamping with force controlled gigaseal formation," says Zambelli. "We will also explore other strategies at the single-cell level, such as the controlled perforation of the cell membrane for local extraction of cytoplasm

"Zambelli and his colleagues are convinced that their technology has great commercial potential. Rejecting offers from well-known manufacturers of atomic force microscopes for the sale of the patent for the FluidFM, they have founded Cytosurge LLC, a company dedicated to commercially develop the instrument.

Today, Zambelli's laboratory contains two prototypes of the instrument, which are being tested in collaboration with biologists.

Virus

Virus

Do viruses and all the other nasties in cyberspace matter? Do they really do much harm? Imagine that no one has updated your anti-virus software for a few months. When they do, you find that your accounts spreadsheets are infected with a new virus that changes figures at random. Naturally you keep backups. But you might have been backing up infected files for months. How do you know which figures to trust? Now imagine that a new email virus has been released. Your company is receiving so many emails that you decide to shut down your email gateway altogether and miss an urgent order from a big customer.

Imagine that a friend emails you some files he found on the Internet. You open them and trigger a virus that mails confidential documents to everyone in your address book including your competitors. Finally, imagine that you accidentally send another company, a report that carries a virus. Will they feel safe to do business with you again? Today new viruses sweep the planet in hours and virus scares are major news. A computer virus is a computer program that can spread across computers and networks by making copies of itself, usually without the user’s knowledge. Viruses can have harmful side effects. These can range from displaying irritating messages to deleting all the files on your computer.

A virus program has to be run before it can infect your computer. Viruses have ways of making sure that this happens. They can attach themselves to other programs or hide in code that is run automatically when you open certain types of files. The virus can copy itself to other files or disks and make changes on your computer. Virus side effects, often called the payload, are the aspect of mostinterest to users. Password-protecting the documents on a particular day, mailing information about the user and machine to an address somewhere are some of the harmful side effects of viruses. Various kinds of viruses include macro virus, parasitic or file virus, Boot virus, E-mails are the biggest source of viruses. Usually they come as attachments with emails.

The Internet caused the spreading of viruses around the globe. The threat level depends on the particular code used in the WebPages and the security measures taken by service providers and by you. One solution to prevent the viruses is anti-virus softwares. Anti-virus software can detect viruses, prevent access to infected files and often eliminate the infection.

Computer viruses are starting to affect mobile phones too. The virus is rare and is unlikely to cause much damage. Anti-virus experts expect that as mobile phones become more sophisticated they will be targeted by virus writers. Some firms are already working on anti-virus software for mobile phones. VBS/Timo-A, Love Bug,Timofonica,CABIR,aka ACE-? and UNAVAILABLE are some of the viruses that affect the mobile phones


BASIC CONCEPTS
What is a virus?
A computer virus is a computer program that can spread across computers and networks by making copies of itself, usually without the user’s knowledge. Viruses can have harmful side-effects. These can range from displaying irritating messages to deleting all the files on your computer.
Evolution of virus
In the mid-1980s Basit and Amjad Alvi of Lahore, Pakistan discovered that people were pirating their software. They responded by writing the first computer virus, a program that would put a copy of itself and a copyright message on any floppy disk copies their customers made. From these simple beginnings, an entire virus counter-culture has emerged. Today new viruses sweep the planet in hours and virus scares are major news
How does a virus infect computers?

A virus program has to be run before it can infect your computer. Viruses have ways of making sure that this happens. They can attach themselves to other programs or hide in code that is run automatically when you open certain types of files. You might receive an infected file on a disk, in an email attachment, or in a download from the internet. As soon as you launch the file, the virus code runs. Then the virus can copy itself to other files or disks and make changes on your computer.
Who writes viruses?
Virus writers don’t gain in financial or career terms; they rarely achieve real fame; and, unlike hackers, they don’t usually target particular victims, since viruses spread too indiscriminately. Virus writers tend to be male, under 25 and single. Viruses also give their writers powers in cyberspace that they could never hope to have in the real world.
Virus side effects(Payload)
Virus side-effects are often called the payload. Viruses can disable our computer hardware, Can change the figures of an accounts spreadsheets at random, Adversely affects our email contacts and business domain, Can attack on web servers…
 Messages -WM97/Jerk displays the message ‘I think (user’s name) is a big stupid jerk!’  Denying access -WM97/NightShade password-protects the current document on Friday 13th. Data theft- Troj/LoveLet-A emails information about the user and machine to an address in the Philippines
. Corrupting data -XM/Compatable makes changes to the data in Excel spreadsheets. Deleting data -Michelangelo overwrites parts of the hard disk on March 6th.
 Disabling Hardware -CIH or Chernobyl (W95/CIH-10xx)
 attempts to overwrite the BIOS on April 26th, making the machine unusable.
 Crashing servers-Melissa or Explore Zip, which spread via email, can generate so much mail that servers crash.
There is a threat to confidentiality too. Melissa can forward documents, which may contain sensitive information, to anyone in your address book. Viruses can seriously damage your credibility. If you send infected documents to customers, they may refuse to do business with you or demand compensation. Sometimes you risk embarrassment as well as a damaged business reputation. WM/Polypost, for example, places copies of your documents in your name on alt.sex usenet newsgroups.
VIRUSES AND VIRUS LIKE PROGRAMMES
Trojan horses
Trojan horses are programs that do things that are not described in their specifications The user runs what they think is a legitimate program, allowing it to carry out hidden, often harmful, functions. For example, Troj/Zulu claims to be a program for fixing the ‘millennium bug’ but actually overwrites the hard disk. Trojan horses are sometimes used as a means of infecting a user with a computer virus.
Backdoor Trojans
A backdoor Trojan is a program that allows someone to take control of another user’s PC via the internet. Like other Trojans, a backdoor Trojan poses as legitimate or desirable software. When it is run (usually on a Windows 95/98 PC), it adds itself to the PC’s startup routine. The Trojan can then monitor the PC until it makes a connection to the internet. Once the PC is on-line, the person who sent the Trojan can use software on their computer to open and close programs on the infected computer, modify files and even send items to the printer. Subseven and Back Orifice are among the best known backdoor Trojans.
Worms
Worms are similar to viruses but do not need a carrier (like a macro or a boot sector).They are subtype of viruses. Worms simply create exact copies of themselves and use communications between computers to spread. Many viruses, such as Kakworm (VBS/Kakworm) or Love Bug (VBS/LoveLet-A), behave like worms and use email to forward themselves to other users.
Boot sector viruses
Boot sector viruses were the first type of virus to appear. They spread by modifying the boot sector, which contains the program that enables your computer to start up. When you switch on, the hardware looks for the boot sector program – which is usually on the hard disk, but can be on floppy or CD – and runs it. This program then loads the rest of the operating system into memory. A boot sector virus replaces the original boot sector with its own, modified version (and usually hides the original somewhere else on the hard disk). When you next start up, the infected boot sector is used and the virus becomes active. You can only become infected if you boot up your computer from an infected disk, e.g. a floppy disk that has an infected boot sector. Many boot sector viruses are now quite old.
Those written for DOS machines do not usually spread on Windows 95, 98, Me, NT or 2000 computers, though they can sometimes stop them from starting up properly. Boot viruses infect System Boot Sectors (SBS) and Master Boot Sectors (MBS). The MBS is located on all physical hard drives. It contains, among other data, information about the partition table (information about how a physical disk is divided into logical disks), and a short program that can interpret the partition information to find out where the SBS is located. The MBS is operating system independent. The SBS contains, among other data, a program whose purpose is to find and run an operating system. Because floppy diskettes are exchanged more frequently than program files boot viruses are able to propagate more effectively than file viruses.Form -A virus that is still widespread ten years after it first appeared.
The original version triggers on the 18th of each month and produces a click when keys are pressed on the keyboard. Parity Boot - A virus that may randomly display the message ‘PARITY CHECK’ and freeze the operating system. The message resembles a genuine error message displayed when the computer’s memory is faulty.
Parasitic virus (File virus)
Parasitic viruses, also known as file viruses, attach themselves to programs (or ‘executables’) and Acts as a part of the program .When you start a program infected with a file virus, the virus is launched first. To hide itself, the virus then runs the original program. The operating system on your computer sees the virus as part of the program you were trying to run and gives it the same rights. These rights allow the virus to copy itself, install itself in memory or release its payload. these viruses Infects over networks.
The internet has made it easier than ever to distribute programs, giving these viruses new opportunities to spread.
 Jerusalem- On Friday 13th deletes every program run on the computer.
 CIH (Chernobyl) - On the 26th of certain months, this virus will overwrite part of the BIOS chip, making the computer unusable. The virus also overwrites the hard disk.
 Remote Explorer - WNT/RemExp (Remote Explorer) infects Windows NT executables. It was the first virus that could run as a service, i.e. run on NT systems even when no-one is logged in. Parasitic viruses infects executables by companion, link, overwrite, insert, prep end, append techniques

a) Companion virus
A companion virus does not modify its host directly. Instead it maneuvers the operating system to execute itself instead of the host file. Sometimes this is done by renaming the host file into some other name, and then grant the virus file the name of the original program. Or the virus infects an .EXE file by creating a .COM file with the same name in the same directory. DOS will always execute a .COM file first if only the program name is given, so if you type “EDIT” on a DOS prompt, and there is an EDIT.COM and EDIT.EXE in the same directory, the EDIT.COM is executed.
b) Linking Virus
A link virus makes changes in the low-level workings of the file system, so that program names do no longer point to the original program, but to a copy of the virus. It makes it possible to have only one instance of the virus, which all program names point to.

Limits and Fits, Tolerance Dimensioning

Limits and Fits, Tolerance Dimensioning

Definitions:nominal size: The size designation used for generalidentification. The nominal size of a shaft and a hole are thesame. This value is often expressed as a fraction.basic size: The exact theoretical size of a part. This isthe value from which limit dimensions are computed. Basic size isa four decimal place equivalent to the nominal size. The number ofsignificant digits imply the accuracy of the dimension.

example: nominal size = 1 1/4basic size = 1.2500

design size: The ideal size for each component (shaft andhole) based upon a selected fit. The difference between the designsize of the shaft and the design size of the hole is equal to theallowance of the fit. The design size of a part corresponds to the Maximum Material Condition (MMC). That is, the largest shaft permitted by the limits and the smallest hole. Emphasis is placed upon the design size in the writing of the actual limit dimension, so the design size is placed in the top position of the pair.

tolerance: The total amount by which a dimension is allowed to vary. For fractional linear dimensions we have assumed a bilateral tolerance of 1/64 inch. For the fit of a shaft/holecombination, the tolerance is considered to be unilateral, that is, it is only applied in one direction from design size of the part. Standards for limits and fits state that tolerances are appliedsuch that the hole size can only vary larger from design size and the shaft size smaller.
basic hole system: Most common system for limit dimensions. In this system the design size of the hole is taken to be equivalent to the basic size for the pair (see above). This means that the lower (in size) limit of the hole dimension is equal to design size. The basic hole system is more frequently used since most hole generating devices are of fixed size (for example, drills, reams, etc.) When designing using purchased components with fixed outer diameters (bearings, bushings, etc.) a basic shaft system may be used.

allowance: The allowance is the intended difference in the sizes of mating parts. This allowance may be: positive (indicated with a "+" symbol), which means there is intended clearance between parts; negative("-"), for intentional interference: or "zero allowance" if the two parts are intended to be the "same size".This last case is common to selective assembly.

The extreme permissible values of a dimension are known as limits. The degree of tightness or looseness between two mating parts that are intended to act together is known as the fit of the parts. The character of the fit depends upon the use of the parts. Thus, the fit between members that move or rotate relative to each other, such as a shaft rotating in a bearing, is considerably different from the fit that is designed to prevent any relative motion between two parts, such as a wheel attached to an axle.

In selecting and specifying limits and fits for various applications, the interests of interchangeable manufacturing require that (1) standard definitions of terms relating to limits and fits be used; (2) preferred basic sizes be selected wherever possible to be reduce material and tool costs; (3) limits be based upon a series of preferred tolerances and allowances; and (4) a uniform system of applying tolerances (bilateral or unilateral) be used.

Introduction to CAN (Controlled Area Network)

Introduction to CAN (Controlled Area Network)

OVERVIEW

CAN was originally developed by the German company, Robert Bosch, for use in cars, to provide a cost-effective communications bus for in-car electronics and as alternative to expensive, cumbersome and unreliable wiring looms and connectors. The car industry continues to use CAN for an increasing number of applications, but because of its proven reliability and robustness, CAN is now also being used in many other control applications. Intra-vehicular communication:
A typical vehicle has a large number of electronic control systems
The growth of automotive electronics is a result of:Customers wish for better comfort and better safety.Government requirements for improved emission controlReduced fuel consumption
Some of such control systemsEngine timingGearbox and carburetor throttle controlAnti-block systems (ABS)Acceleration skid control (ASC)

The complexity of the functions implemented by these electronic control systems necessitates communication between them.In addition, a number of systems are being developed which will cover more than one device. For exampleASC requires the interplay of the engine timing and carburetor control in order to reduce torque when drive wheel slippage occurs.In the electronic gearbox control, the ease of gear changing can be improved by a brief adjustment to ignition timing

How do we connect these control devices?
With conventional systems, data is exchanged by means of dedicated signal lines.
But this is becoming increasingly difficult and expensive as control functions become ever more complex.

In the case of complex control systems in particular, the number of connections cannot be increased much further.

Solution: Use Field bus networks for connecting the control devices

FIELD BUS NETWORKS

Field buses are communication technologies and products used in vehicular, automation and process control industries.
Proprietary Field busesProprietary Field buses are an intellectual property of a particular company or body.

Open Field busesFor a Field bus to be Open, it must satisfy the following criteria.The full Field bus Specification must be published and available at a reasonable price. Critical ASIC components must be available, also at a reasonable price. Well defined validation process, open to all of the Field bus users.

Field bus Advantages:

I.Reduces the complexity of the control system in terms of hardware outlay.
II.Resulting in the reduced complexity of the control system, project design engineering is made simpler, more efficient and conversely less expensive.

III.By selecting a recognized and well established system, this will make the Fieldbus equipment in you plant or plants interchangeable between suppliers.

IV.The need to be concerned about connections, compatibility and other potential problems is eradicated.

What constitutes a Field bus?The specification of a Field bus should ideally cover all of the seven layers of the OSI model as shown below,.

FEATURES OF CANCAN features are as follows:-

CAN is a robust protocol – essential for automotive applicationsSO 11898 and SAE/J2411 are open standardsWell documented and fully supported worldwideChoice of three CAN physical layer optionsHigh-speed (HS)for high data ratesFault-tolerant (FT)for additional robustnessSingle-wire (SW)for minimum wiringAny node can access the bus when the bus is quiet.Non- destructive bit-wise arbitration to allow 100% use of bandwidth without loss of data.Variable message priority based on 11-bit (or 29 bit) packet identifier.Peer- to-Peer and multi-cast receptionAutomatic error detection, signaling and retries.Data packets 8 bytes long

BENEFITS OF CAN

Can is a fast serial Bus that designed to provide An efficientReliable and Very economical link between sensors & actuatorsCan uses a twisted pair cables to communicate at speed up to 1 Mbit/s up to 40 devices.Originally CAN is developed to simplify the wiring in automobiles.CAN field buses are now used in machine and factory automation products as well.

CAN History

In the early 1980s, engineers at Bosch were evaluating existing serial bus systems regarding their possible use in passenger cars. Because none of the available network protocols were able to fulfill the requirements of the automotive engineers, Uwe Kiencke started the development of a new serial bus system in 1983.

The new bus protocol was mainly supposed to add new functionality – the reduction of wiring harnesses was just a by-product, but not the driving force behind the development of CAN. Engineers from Mercedes-Benz got involved early on in the specification phase of the new serial bus system, and so did Intel as the potential main semiconductor vendor. Professor Dr. Wolfhard Lawrenz from the University of Applied Science in Braunschweig-Wolfenbüttel, Germany, who had been hired as a consultant, gave the new network protocol the name ‘Controller Area Network’. Professor Dr. Horst Wettstein from the University of Karlsruhe also provided academic assistance. In February of 1986, CAN was born: at the SAE congress in Detroit, the new bus system developed by Bosch was introduced as ‘Automotive Serial Controller Area Network’. Uwe Kiencke, Siegfried Dais and Martin Litschel introduced the multi-master network protocol. It was based on a non-destructive arbitration mechanism, which would grant bus access to the message with the highest priority without any delays.

There was no central bus master. Furthermore, the fathers of CAN – the individuals mentioned above plus Bosch employees Wolfgang Borst, Wolfgang Botzenhard, Otto Karl, Helmut Schilling, and Jan Unruh – had implemented several error detection mechanisms. The error handling also included the automatic disconnection of faulty bus nodes in order to keep up the communication between the remaining nodes. The transmitted messages were not identified by the node address of the transmitter or the receiver of the message (as in almost all other bus systems), but rather by their content. The identifier representing the content of the message also had the function of specifying the priority of the message within the system.
A lot of presentations and publications describing this innovative communication protocol followed, until in mid 1987 – two months ahead of schedule – Intel delivered the first CAN controller chip, the 82526.

It was the very first hardware implementation of the CAN protocol. In only four years, an idea had become reality. Shortly thereafter, Philips Semiconductors introduced the 82C200. These two earliest ancestors of the CAN controllers were quite different concerning acceptance filtering and message handling. On one hand, the FullCAN concept favored by Intel required less CPU load from the connected micro-controller than the BasicCAN implementation chosen by Philips. On the other hand, the FullCAN device was limited regarding the number of messages that could be received. The BasicCAN controller also required less silicon. In today’s CAN controllers, the ‘grandchildren’, very often different concepts of acceptance filtering and message handling have been implemented in the same module, making the misleading terms BasicCAN and FullCAN obsolete.

IMPLEMENTATION OF CAN

Communication is identical for all implementations of CAN. However, there are two principal hardware implementations. The two implementations are known as Basic CAN and Full CAN.
Basic CAN In Basic CAN configurations there is a tight link between the CAN controller and the associated microcontroller. The microcontroller, which will have other system related functions to administer, will be interrupted to deal with every CAN message.

Full CANFull CAN devices contain additional hardware to provide a message "server" that automatically receives and transmits CAN messages without interrupting the associated microcontroller. Full CAN devices carry out extensive acceptance filtering on incoming messages, service simultaneous requests, and generally reduce the load on the microcontroller.
Network SizesThe number of nodes that can exist on a single network is, theoretically, limited only by the number of available identifiers. However, the drive capabilities of currently available devices impose greater restrictions. Depending on the device types, up to 32 or 64 nodes per network is normal, but at least one manufacturer now provides devices that will allow networks of 110 nodes.

HOW CAN WORKS ?

Principle

Data messages transmitted from any node on a CAN bus do not contain addresses of either the transmitting node, or of any intended receiving node.Instead, the content of the message (e.g. Revolutions per Minute, Hopper Full, X-ray Dosage, etc.) is labeled by an identifier that is unique throughout the network. All other nodes on the network receive the message and each performs an acceptance test on the identifier to determine if the message, and thus its content, is relevant to that particular node. If the message is relevant, it will be processed; otherwise it is ignored. The unique identifier also determines the priority of the message. The lower the numerical value of the identifier, the higher the priority. In situations where two or more nodes attempt to transmit at the same time, a non-destructive arbitration technique guarantees that messages are sent in order of priority and that no messages are lost.

Bit encodingCAN use Non Return to Zero (NRZ) encoding (with bit-stuffing) for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance.
The physical busThe two wire bus is usually a twisted pair (shielded or unshielded). Flat pair (telephone type) cable also performs well but generates more noise itself, and may be more susceptible to external sources of noise.

The CAN protocol is an international standard defined in the ISO 11898. Beside the CAN protocol itself the conformance test for the CAN protocol is defined in the ISO 16845, which guarantees the interchangeability of the CAN chips.

CAN is based on the “broadcast communication mechanism”, which is based on a message-oriented transmission protocol. It defines message contents rather than stations and station addresses. Every message has a message identifier, which is unique within the whole network since it defines content and also the priority of the message.

This is important when several stations compete for bus access (bus arbitration), as a result of the content-oriented addressing. This allows for a modular concept and also permits the reception of multiple data and the synchronization of distributed processes. Also, data transmission is not based on the availability of specific types of stations, which allows simple servicing and upgrading of the network.

Message formats

CAN distinguishes four message formats: data, remote, error, and overload frames. Here we limit the discussion to the data frame. A data frame begins with the start-of-frame (SOF) bit. It is followed by an eleven-bit identifier and the remote transmission request (RTR) bit. The identifier and the RTR bit form the arbitration field. The control field consists of six bits and indicates how many bytes of data follow in the data field. The data field can be zero to eight bytes. The data field is followed by the cyclic redundancy checksum (CRC) field, which enables the receiver to check if the received bit sequence was corrupted. The two-bit acknowledgment (ACK) field is used by the transmitter to receive an acknowledgment of a valid frame from any receiver.

The end of a message frame is signalled through a seven-bit end-offrame (EOF). There is also an extended data frame with a twenty-nine-bit identifier (instead of eleven bits).The CAN protocol was internationally standardized in 1993 as ISO 11898-1. The development of CAN was mainly motivated by the need for new functionality, but it also reduced the need for wiring. The use of CAN in the automotive industry has caused mass production of CAN controllers. Today, CAN controllers are integrated on many microcontrollers and available at a low cost.

CAN ARCHITECTURE

Any node can access the bus when the bus is quiet
Non-destructive bit-wise arbitration to allow 100% use of the bandwidth without loss of data
Variable message priority based on 11-bit (or 29 bit) packet identifier
Peer-to-peer and multi-cast reception
Automatic error detection, signalling and retries
Data packets 8 bytes long
ERROR HANDLING PERFORMANCE OF CAN
Error detection and error handling are important for the performance of CAN. Because of complementary error detection mechanisms, the probability of having an undetected error is very small. Error detection is done in five different Vehicle Applications of Controller Area Network 7 ways in CAN: bit monitoring and bit stuffing, as well as frame check, ACK check, and CRC. Bit monitoring simply means that each transmitter monitors the bus level, and signals a bit error if the level does not agree with the transmitted signal. (Bit monitoring is not done during the arbitration phase.)

After having transmitted five identical bits, a node will always transmit the opposite bit. This extra bit is neglected by the receiver. The procedure is called bit stuffing, and it can be used to detect errors. The frame check consists of checking that the fixed bits of the frame have the values they are supposed to have, e.g., EOF consists of seven recessive bits. During the ACK in the message frame, all receivers are supposed to send a dominant level. If the transmitter, which transmits a recessive level, does not detect the dominant level, then an error is signalled by the ACK check mechanism.

Finally, the CRC is that every receiver calculates a checksum based on the message and compares it with the CRC field of the message. Every receiver node obviously tries to detect errors within each message. If an error is detected, it leads to an immediate and automatic retransmission of the incorrect message. In comparison to other network protocols, this mechanism leads to high data integrity and a short error recovery time. CAN thus provides elaborate procedure for error handling, including retransmission and reinitialization. The procedures have to be studied carefully for each application to ensure that the automated error handling is in line with the system requirements.

APPLICATIONS

CAN networks can be used as an embedded communication system for microcontrollers as well as an open communication system for intelligent devices. The CAN serial bus system, originally developed for use in automobiles, is increasingly being used in industrial field bus systems, the similarities are remarkable. In both cases some of the major requirements are: low cost, the ability to function in a difficult electrical environment, a high degree of real-time capability and ease of use.Some users, for example in the field of medical engineering, opted for CAN because they have to meet particularly stringent safety requirements.

Similar problems are faced by manufacturers of other equipment with very high safety or reliability requirements (e. g. robots, lifts and transportation systems). CAN controllers and interface chips are physically small. They are available as low-cost, off-the-shelf components. They will operate at high, real-time speeds, and in harsh environments. All these properties have led to CAN also being used in a wide range of applications other than the car industry. The benefits of reduced cost and improved reliability that the car industry gains by using CAN are now available to manufacturers of a wide range of products.

For example:

• Marine control and navigation systems

•Elevator control systems

• Agricultural machinery

• Production line control systems

• Machine tools

• large optical telescopes

• Photo copiers

• Medical systems

• Paper making and processing machinery

VEHICLE APPLICATIONS OF CAN

The Controller Area Network (CAN) is a serial bus communications protocol developed by Bosch in the early 1980s. It defines a standard for efficient and reliable communication between sensor, actuator, controller, and other nodes in real-time applications. CAN is the de facto standard in a large variety of networked embedded control systems.

The early CAN development was mainly supported by the vehicle industry: CAN is found in a variety of passenger cars, trucks, boats, spacecraft, and other types of vehicles. The protocol is also widely used today in industrial automation and other areas of networked embedded control, with applications in diverse products such as production machinery, medical equipment, building automation, weaving machines & wheelchairs.In the automotive industry, embedded control has grown from stand-alone systems to highly integrated and networked control systems. By networking electro-mechanical subsystems, it becomes possible to modularize functionalities and hardware, which facilitates reuse and adds capabilities. Fig. 1 shows an example of an electronic control unit (ECU) mounted on a diesel engine of a Scania truck. The ECU handles the control of engine, turbofan, etc. but also the CAN communication. Combining networks and mechatronic modules makes it possible to reduce both the cabling and the number. The work of K. H. Johansson was partially supported by the European Commission through the ARTIST2 Network of Excellence on Embedded Systems Design, by the Swedish Research Council, and by the Swedish Foundation for Strategic Research through an Individual Grant for the Advancement of Research Leaders.
The work of M. T¨orngren was partially supported by the European Commission through ARTIST2 and by the Swedish Foundation for Strategic Research through the project SAVE of connectors, which facilitates production and increases reliability. Introducing networks in vehicles also makes it possible to more efficiently carry out diagnostics and to coordinate the operation of the separate subsystems.

Heavy Vehicles

Most existing vehicle model libraries are designed primarily for cars. Heavy vehicles have a number of sub-systems which are not present in passenger cars. Particularly the engine/transmission system includes de-vices like an exhaust brake and possibly a retarder. Further, the cooling system also has a more prominent role than in cars, and coolant is often used both by the engine and the transmission.

Signalling Bus

A key issue in an architecture which contains both physical plant and controller models is the handling of electrical signals. The controllers need to exchange data among themselves and they need to exchange signals with sensors and actuators. For our applications the actual signalling behaviour is not that important, an ideal communications model is sufficient. For the communication between a plant and its controller, standard library in-ports and out-ports are used. The communication between the controllers was a tougher case. Two implementations of the same controller may not have the same signalling needs, thus it must be possible to change the set of signals sent between control units. Separate input and output ports for all links between control units in the vehicle would create an un-decipherable graphical mess. Some type of signalling bus is needed. Both the standard library bus connectors and the type of bus used in the vehicle modelling architecture proposal by Tiller Etal were evaluated. We did not find enough information about the inter-controller communication in the Tiller paper to implement that system. Our main problem was to find a way of having compatible connectors in all controllers, without modifying the code of every controller when a signal was added to the bus. The standard library bus does not solve that problem, since it requires all signals to be declared in the connector. Eventually we chose a simpler solution based on a common connector called ”CAN” with a replace-able variable, called ”protocol”, which contains all the signals. The protocol variable can easily be redeclared into a type which contains exactly the signals broad-cast on the bus in a particular model. Different implementations of the CAN connector are used for different signal buses in the vehicle.

Most of our control units are implemented through external function calls, thus the drawback of having no convenient graphical way of converting a signal from inport/ outport to bus format is minor.